In the manufacturing process of a semiconductor device or a flat panel display (FPD), a plasma is widely used in a process such as etching, deposit, oxidation, sputtering or the like since it has a good reactivity with a processing gas at a relatively low temperature. In such plasma process, the plasma is mostly generated by a radio frequency (RF) discharge in the megahertz range. Specifically, the plasma generated by the RF discharge is classified into a capacitively coupled plasma and an inductively coupled plasma.
Typically, an inductively coupled plasma processing apparatus includes a processing chamber, at least a portion (e.g., a ceiling portion) of which is formed of a dielectric window; and a coil-shaped RF antenna provided outside the dielectric window, and an RF power is supplied to the RF antenna. The processing chamber serves as a vacuum chamber capable of being depressurized, and a target substrate (e.g., a semiconductor wafer, a glass substrate or the like) to be processed is provided at a central portion of the chamber. Further, a processing gas is introduced into a processing space between the dielectric window and the substrate.
As an RF current flows though the RF antenna, an RF magnetic field is generated around the RF antenna, wherein the magnetic force lines of the RF magnetic field travel through the dielectric window and the processing space. The temporal alteration of the generated RF magnetic field causes an electric field to be induced azimuthally. Moreover, electrons azimuthally accelerated by the induced electric field collide with molecules and/or atoms of the processing gas, to thereby ionize the processing gas and generate a plasma in a doughnut shape.
By increasing the size of the processing space in the chamber, the plasma is efficiently diffused in all directions (especially, in the radical direction), thereby making the density of the plasma on the substrate uniform. However, the uniformity of the plasma density on the substrate that is obtained by merely using a typical RF antenna is generally insufficient for the plasma process.
Accordingly, even as for the inductively coupled plasma processing apparatus, it becomes one of the most important factors to improve the uniformity of the plasma density on the substrate, since it determines the uniformity and the reproducibility of the plasma process itself and, furthermore, the manufacturing production yield.
Typically, in the plasma processing apparatus, the plasma density may be made uniform in two, i.e., azimuthal and radial directions.
As for the uniformity in the azimuthal direction, since the RF antenna includes an RF input-output terminal connected through an RF power supply line to an RF power supply in a loop thereof, it is inevitable to employ a nonaxisymmetric antenna configuration. This serves as a main factor that makes the plasma density nonuniform in the azimuthal direction. Accordingly, the uniformity in the azimuthal direction can conventionally be improved by increasing the number of nonaxisymmetric or singularity locations of the RF antenna at a regular interval in the same direction (see, e.g., U.S. Pat. No. 5,800,619). Alternatively, by using two-layered series-connected coils as the RF antenna, wherein the RF power supply wire-connected locations (input-output terminals) provided in the upper coil are hidden behind the lower coil, the locations may not be electromagnetically seen from the plasma (see, e.g., Japanese Patent Application Publication No. 2003-517197).
Moreover, as for the radial direction, the plasma density distribution characteristics (profile) of the plasma generated in the doughnut shape around the dielectric window in the chamber are important and, thus, the profile of the core plasma density distribution determines the uniformity of the plasma density distribution that can be obtained on the substrate after the diffusion. In this regard, the conventional method for dividing the RF antenna into a plurality of segments in the radial direction is mostly employed. Further, such RF antenna dividing method includes a first method for individually supplying RF powers to the respective antenna segments (see, e.g., U.S. Pat. No. 5,401,350); and a second method for controlling the division ratio of the RF power that is divided from one RE power supply to all the antenna segments by changing each impedance of the antenna segments in an additional circuit such as a capacitor or the like (see, e.g., U.S. Pat. No. 5,907,221).
However, such conventional methods for improving the uniformity of the plasma density distribution is disadvantageous in that it is difficult to manufacture any type of RF antenna for improving the uniformity in the azimuthal or radial direction due to its complex configuration; or the loads of the RF power supply system (RF power supply and matcher) are increased.
Especially, the conventional method for improving the uniformity in the azimuthal direction of the plasma density distribution has the restriction in the accuracy and improvement of the uniformity since an antenna portion (e.g., the lower antenna) attributable to the generation of inductive coupling plasma does not have an exactly axisymmetric shape.